A disease outbreak investigation by Oregon state and Marion County public health officials has led to a multi-state recall of thousands of pounds of frozen oysters, officials at the Oregon Department of Human Services Public Health Division said today.

The recall, announced today by the U.S. Food and Drug Administration, covers a large lot of frozen oysters on the half-shell imported from Korea.

"This is a great example of how public health programs work together to prevent illness," said Mel Kohn, M.D., state epidemiologist in the DHS Public Health Division.

Kohn said the investigation unfolded rapidly, starting late on Nov. 22. The Marion County Health Department first heard reports of illnesses following a private reception in Woodburn. County and state public health officials worked late into the evening, collecting information, developing a questionnaire and interviewing a sample of the 250 people who attended the reception.

By Thanksgiving morning, interviews were completed and questionnaire data had been analyzed. The result was clear: people had been sickened by eating oysters, which were served raw on the half shell.

"Eating raw shellfish is always risky, regardless of their origin or the time of year," said Kohn. "Whether they come fresh or frozen, it's always best to cook shellfish thoroughly."

Subsequent specimen testing at the Oregon State Public Health Laboratory in Portland confirmed the infection was a norovirus. And while there were no reports of serious illness or hospitalization, Kohn said it is estimated about 40 people were affected.

Oregon notified other state and federal officials on Thanksgiving. The Oregon Department of Agriculture and the FDA worked with the DHS Public Health Division to trace the oysters through a chain of suppliers to their source in Korea. Other portions of the same lot were sold in Oregon, California, Colorado, Texas and Nevada, but no other illnesses have been reported, according to Kohn.

On Dec. 7, an FDA lab confirmed the presence of noroviruses in samples of frozen oysters from the same production lot, and the recall became official. More information about the recall can be found on the FDA's Web site.

Noroviruses, also known as Norwalk-like viruses, are the most common cause of acute gastrointestinal illness in Oregon and the United States. Oregon has confirmed more 100 noroviral outbreaks this year, Kohn said.

"In healthy people, the infection typically lasts one or two days, but the infection is not trivial," Kohn said. "Some people become completely incapacitated by the symptoms, which include vomiting and diarrhea."

This investigation reflects state and local communicable disease and food safety programs working together, Kohn noted, and represents one of many public health activities within DHS that focus on prevention and helping people manage their health so they can be as productive and healthy as possible. More information about the DHS communicable disease program is on the Web.